The invention relates to the field of optical devices, in particular liquid crystal imagers, as well as the mirrors associated with these optical devices. The optical device is angled, and includes at least one lamp and a channel guiding at least some of the light coming from the lamp, as well as a mirror in an angled part of the optical device, consisting of a sheet which is folded so that, on the one hand, it can be partially introduced into the channel and, on the other hand, once introduced into the channel and immobilized therein, it can reflect some of the light coming from the lamp into a determined direction. The invention may, in particular, be applied to liquid crystal imagers for military aircraft.